Today I set up a short (900 mm) test track to see whether the locos I recently retrieved from five decades of storage would run. First off, I discovered that I'd better clean the track (also in storage since the late '60s). Used alcohol swabs (thanks to a tip I found on here; I wouldn't have thought of it myself); they worked a treat.
Tried my 3016 Schienenbus, which toddled back and forth nicely after some initial hesitation.
Sadly, the late-'50s-vintage 3001 elok didn't want to move. I suspect years in a trunk in a humid garage have done it no good; the side rods are rusty, so heaven knows what the rest of the mech is like. However, it is getting power: the reversing solenoid works. So I shall take the body off and see if I can clean the mech up; if that doesn't work, I shall send it to a dealer to see if it can be rescued.
Has anyone used WD40 to clean a mech before relubricating?

I use WD40 all the time.
But I DO wipe clean afterwards with a dry cloth, and avoid touching plastic- and rubber-parts with it!

I tried some lighter fluid on the gears. It seems to have freed things up a little. The loco now jerks a bit when I send a reversing pulse from the controller, but still no sustained motion.

By George, I think we may have it. Thank you.
After applying a dose of lighter fluid yesterday (and removing the brushes), I tried turning the wheels, but they wouldn't budge, and I didn't want to use too much force.
However, I have just gone through the process again, and this time (after a little persuasion), everything started to turn.
I shall wait a few hours for the fluid to evaporate and then try the loco on the track again.
Fingers crossed ...